In the field of magnetic recording devices, recording has been accomplished at ever-increasing densities in recent years, and thin film magnetic heads are in use for recording and reproduction. For example, a thin film of Permalloy comprising Ni and Fe is widely used as a magnetic thin film for forming the magnetic core layer of such thin film magnetic heads. It is required that the magnetic thin film for forming the magnetic core layer have excellent soft magnetic properties, especially high magnetic permeability at high frequencies, so as to exhibit improved switching characteristics at high frequencies.
Generally, high magnetic permeabilities can be obtained effectively by imparting uniaxial magnetic anisotropy to the magnetic thin film so that the direction of track width of the magnetic gap becomes the direction of easy axis of magnetization. The magnetic thin film is given uniaxial magnetic anisotropy when formed as subjected to an external magnetic field.
Further for controlling the uniaxial magnetic anisotropy, it is suitable to form magnetic thin films having a negative magnetostriction constant in the range of -1.times.10.sup.-6 to -5.times.10.sup.-6 as is already known. For example, Unexamined Japanese Patent Publication HEI 1-201812 discloses that the magnetostriction constant of the magnetic thin film is made smaller than -5.times.10.sup.-6. Unexamined Japanese Patent Publication SHO 55-101124 discloses the reason for this; since tensile stress acts on the magnetic thin film in the direction of width of the track, the tensile stress hinders magnetization rotation with the result that the direction of easy axis of magnetization becomes the direction of width of the track.
Unexamined Japanese Patent Publication HEI 2-81409 discloses that for forming an NiFe thin film having excellent magnetic properties by the conventional common sputtering method or magnetron sputtering method, it is useful to limit the Fe content to the range of 16.5 to 17.5 wt. %.
However, difficulty is encountered in recent years in controlling the magnetic anisotropy by stress because thin film magnetic heads are diminished to not greater than 10 .mu.m in track width and are consequently reduced to not greater than several micrometers in the depth of the magnetic gap. Further with thin film magnetic heads of the composite type wherein a magneto-resistive head is formed before an inductive magnetic head is formed, the magnetic thin film of the inductive magnetic head is subjected to complex stresses.
The NiFe thin film of the above-mentioned composition is excellent as a magnetic core material in that it has a high magnetic permeability and a small coercive force, but the thin film is not suited to high-density recording because the low Fe content leads to a small saturation magnetic flux density and renders the magnetic core layer liable to saturation during recording.